The disclosure of Japanese Patent Application No. 2000-401609 filed on Dec. 28, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a rollover determining apparatus and methods for determining whether a vehicle is about to roll over.
2. Description of Related Art
A rollover determining apparatus designed to determine whether a vehicle is about to roll over based on the roll angle and the roll rate of the vehicle is conventionally known. It is also known that as a vehicle turns a comer, an occupant is likely to shift closer to a side portion of the vehicle. Therefore, if a vehicle rolls over during the turn, the deployment space for an airbag installed in a side portion of the vehicle may be reduced. Thus, an apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-9599 determines whether the vehicle is turning based on the steering angle. When the vehicle is not turning, the apparatus determines whether the vehicle is about to roll over based on the roll angle and the roll rate. When the vehicle is turning, the apparatus determines in an earlier period whether the vehicle is about to roll over, factoring in the lateral acceleration.
The rollover of a vehicle includes different types of rollovers like, for example, a flip-over due to a run upon an inclined surface and the like, as well as a turn-over due to sharp turning of the vehicle. Therefore, the determination regarding whether the vehicle is about to roll over based only on whether the vehicle is turning, as in the conventional technology, is not sufficient to make a precise determination of whether various types of rollovers will occur.
Accordingly, it is an object of the invention to appropriately distinguish types of rollovers, and to improve the precision in the rollover determination in accordance with the distinguished types of rollovers.
One aspect of the invention is a rollover determining apparatus and methods for determining whether a vehicle is about to roll over. The apparatus includes a controller that distinguishes a type of rollover that is likely to occur to the vehicle based on a physical quantity that indicates a state of the vehicle, and that determines that the vehicle is about to rollover if the state of the vehicle meets a determination condition corresponding to the type of rollover distinguished.
This rollover determining apparatus is able to distinguish the type of rollover that is likely to occur to the vehicle based on the physical quantity that indicates the state of the vehicle. Furthermore, the apparatus determines whether a rollover is about to occur based on the determination condition that is appropriate (that exhibits a characteristic change) in accordance with the type of rollover distinguished. Therefore, it becomes possible to more precisely determine whether a rollover is about to occur.
Specifically, the rollover determining apparatus may determine whether one of a flip-over, turn-over and trip-over will occur to the vehicle based on the lateral acceleration and the roll angle of the vehicle.
Furthermore, the controller may determine whether the state of the vehicle, which is indicated by a predetermined physical quantity that corresponds to the type of distinguished rollover, is in a rollover region that is determined by a predetermined threshold line, and may change the threshold line in accordance with a magnitude of another physical quantity that is different from the predetermined quantity and that corresponds to the type of distinguished rollover.
Thus, after appropriately distinguishing the type of rollover, the rollover determining apparatus appropriately stores physical quantities that appear at the time of a rollover in accordance with the characteristics of the type of the rollover. Using these physical quantities, the state of the vehicle is determined. Then, a rollover region is indicated beforehand by a predetermined threshold line. Therefore, it is possible to appropriately determine whether the vehicle is about to roll over. The threshold line is changed by a physical quantity that is different from the aforementioned physical quantity. Therefore, it becomes possible to more precisely determine whether the vehicle is about to roll over.
According to a further aspect of the invention, a rollover determining apparatus and method determines whether the vehicle is about to roll over. The apparatus includes a lateral acceleration detector that detects and outputs a lateral acceleration of the vehicle. Furthermore, a roll rate detector detects a roll rate of the vehicle, a first low-pass filter is connected to the lateral acceleration detector and passes a frequency that is at most a first cutoff frequency, and a second low-pass filter is connected to the lateral acceleration detector and passes a frequency that is at most a second cutoff frequency that is higher than the first cutoff frequency. Finally, a controller can determine that the vehicle is about to roll over if the following criteria occurs: (a) a state of the vehicle indicated by the lateral acceleration filtered by the first low-pass filter and a roll rate of the vehicle detected enters a rollover region determined by a first threshold line that prescribes a relationship between the lateral acceleration and the roll rate where the lateral acceleration filtered by the second low-pass filter is at most a predetermined threshold; and (b) if the state of the vehicle indicated by the lateral acceleration filtered by the second low-pass filter and the roll rate of the vehicle detected enters a rollover region determined by a second threshold line prescribing a relationship between the lateral acceleration and the roll rate where the lateral acceleration filtered by the second low-pass filter is greater than the predetermined threshold.
The controller may determine whether one of a flip-over, a turn-over and a trip-over is the type of rollover that will occur to the vehicle. If the type of rollover is determined to be a trip-over, the controller performs an additional rollover determination.
As mentioned above, the trip-over can occur when a vehicle skids on dirt or a pavement surface and then rolls over due to, for example, accumulation of sand, earth, etc., on the outer side of a wheel, or in which a vehicle rolls over due to impingement of a wheel on a curb or the like. The trip-over needs to be distinguished from the case where an object impacts on a side portion of a vehicle (generally-termed side collision). Where a trip-over occurs in which the vehicle rolls over due to an impingement of a wheel on a curb or the like, and where an object impacts a side portion of the vehicle, a signal with a relatively high frequency and a great amplitude appears in the output of the lateral acceleration detector (lateral acceleration sensor). In contrast, when the vehicle rolls over skidding on dirt or a pavement surface, such a signal rarely appears.
To classify such signals having relatively high frequencies into two types, the first cutoff frequency and the second cutoff frequency that is higher than the first cutoff frequency are set. A lateral acceleration with a relatively high frequency is detected, and is classified with a threshold value so that the threshold line is changed. Therefore, a trip-over where the vehicle rolls over skidding on dirt or a pavement surface can be determined in an early period. It also becomes possible to discriminate between a trip-over caused by an impingement of a wheel on a curb or the like and an impact of an object upon a side portion of the vehicle.
A further aspect of the invention provides a rollover determining method for determining whether a vehicle is about to roll over. The method includes the steps of: (a) distinguishing a type of rollover that is likely to occur to the vehicle based on a lateral acceleration of the vehicle and a roll angle of the vehicle; (b) determining whether the state of the vehicle indicated by a predetermined physical quantity corresponding to the type of distinguished rollover is in a rollover region determined by a predetermined threshold line; and (c) changing the threshold line in accordance with a magnitude of another physical quantity that is different from the predetermined physical quantity and that corresponds to the type of distinguished rollover.
According to this determining method, a type of rollover that is likely to occur to the vehicle can be distinguished based on the lateral acceleration of the vehicle and the roll angle of the vehicle, in the process of determining whether a rollover is about to occur. Furthermore, it is determined whether a rollover is about to occur based on a determination condition that is appropriate (that exhibits a characteristic change) and that corresponds to the type of distinguished rollover. Therefore, it becomes possible to appropriately determine whether a rollover is about to occur.
A further aspect of the invention provides a rollover determining method for determining whether the vehicle is about to roll over, which includes the steps of: (a) detecting a lateral acceleration of the vehicle; (b) detecting a roll rate of the vehicle; (c) acquiring a waveform of a first lateral acceleration formed by a frequency that is at most a first predetermined frequency, from a waveform of the lateral acceleration of the vehicle detected; (d) acquiring a waveform of a second lateral acceleration formed by a frequency that is at most a second predetermined frequency that is higher than the first predetermined frequency, from the waveform of the lateral acceleration of the vehicle detected; and (e) determining that the vehicle is about to roll over if a state of the vehicle enters a rollover region determined by a first threshold line prescribing a relationship between the first lateral acceleration and the roll rate in a case where the second lateral acceleration is at most a predetermined threshold, or determining that the vehicle is about to roll over if the state of the vehicle enters a rollover region determined by a second threshold line prescribing a relationship between the second lateral acceleration and the roll rate in a case where the second lateral acceleration is greater than the predetermined threshold.
According to this method, a trip-over in which the vehicle rolls over skidding on dirt or a pavement surface can be determined in an early period. It also becomes possible to distinguish between a trip-over caused by an impingement of a wheel on a curb or the like and an impact of an object upon a side portion of the vehicle.